Problem: $-7l - 10m + 10n - 1 = -3m - 9n + 10$ Solve for $l$.
Explanation: Combine constant terms on the right. $-7l - 10m + 10n - {1} = -3m - 9n + {10}$ $-7l - 10m + 10n = -3m - 9n + {11}$ Combine $n$ terms on the right. $-7l - 10m + {10n} = -3m - {9n} + 11$ $-7l - 10m = -3m - {19n} + 11$ Combine $m$ terms on the right. $-7l - {10m} = -{3m} - 19n + 11$ $-7l = {7m} - 19n + 11$ Isolate $l$ $-{7}l = 7m - 19n + 11$ $l = \dfrac{ 7m - 19n + 11 }{ -{7} }$ Swap the signs so the denominator isn't negative. $l = \dfrac{ -{7}m + {19}n - {11} }{ {7} }$